The present invention relates generally to wireless communication systems, and more particularly to a method and system for detecting the presence of on-off signaling in a wireless communications network.
Quick paging channel (QPCH) is an uncoded channel used in CDMA based telecommunication networks for transferring on-off signaling. The channel carries various indicators such as paging indicators, broadcast indicators, and configuration change indicators. The discussion below will use a specific indicator such as the paging indicator as an example, it is understood that whatever can be applied to the paging indicator can also be applied to other indicators carried by the QPCH.
In a wireless communications network, a mobile terminal remains in an idle mode to conserve battery power when there is neither voice nor data call. In the idle mode, the mobile terminal wakes up periodically for a short period typically in the order of milliseconds to monitor a paging indicator to detect whether there is a paging made to the mobile terminal. A relative simple predetermined algorithm is typically used to decide whether the paging indicator indicates that there is an ongoing or an up-and-coming voice or data call. If the outcome of the predetermined algorithm is affirmative, the mobile terminal switches on to decode information communicated through a common channel, which may contain a dedicated or broadcast message in a temporal period of up to 100 ms. If the final determination based on the simple algorithm is negative, the mobile terminal returns to a “sleep mode”, wherein most of the mobile terminal's components are turned off to conserve battery power while keeping a few critical components on to maintain basic timing requirement during the “sleep mode”. As known by those skilled in the art, the more often the mobile terminal has to decode information in the common channel, the more power the mobile terminal must consume. As such, there is a need to increase standby time, or the amount of time that the mobile terminal is in “sleep mode”.
To increase the standby time, a wireless communication system that regularly communicates with the mobile terminal transmits the same paging indicator several times over time to indicate whether there is a paging to the mobile terminal. For example, 3rd Generation Partnership Project 2 describes a quick paging channel designed for this purpose in a CDMA2000 environment. “Physical Layer Standard for CDMA2000 Spread Spectrum Systems,” 3GPP2 C.S0002, March, 2000. See also, “Upper Layer (Layer 3) Signaling Standard for CDMA2000 Spread Spectrum Systems (2000)”, 3GPP2 C.S0005, March, 2000. The QPCH indicators are normally on/off keyed to reduce transmission power. The paging indicators are used to signal the mobile terminal about the presence of a paging message in a predetermined paging slot in the QPCH. If the paging indicator is on, the mobile terminal should wake up and be able to receive the paging. If the paging indicator is off, the mobile terminal can continue to stay in idle to save power. The indicator is repeated once to obtain temporal fading diversity information.
To conserve battery power, it is critical to detect the presence of the paging indicator reliably and efficiently. Due to the presence of noise and fading in aerial communications, the signal-to-noise ratio (SNR) may become very low, a condition that renders any detection mechanism a challenging task. There are generally two types of errors associated with paging. A type I error, a false alarm error, is an incorrect paging detection that may cause a false alarm that in turn causes more battery power. A type II error, a miss error, is an incorrect detection that missed a voice/data call. In wireless communication systems, the detection mechanism has to be designed such that false alarms are minimized without exponentially increasing the miss rate.
A single-stage detection mechanism is disclosed in prior art references wherein one threshold is set for a given false alarm and is to maximize the detection probability. See more in “Fundamentals of Statistical Signal Processing: Detection Theory”, Prentice Hall PTR, 1st Edition, March 1993. However, because only a single threshold is used while the channel gain ratio is changing, the mechanism cannot feasibly minimize the false alarm and miss rate simultaneously for multi-stage paging indicator detection. Other prior methods, while addressing some of the aforementioned issues, are not efficient in a multi-stage detection of paging indicators.
Existing paging detection methods don't utilize the known Signal-to-Noise Ratio (SNR) information to enhance the detection performance. In fact, most of the designs are usually made for dealing with the worst-case scenario. For example, if the design was to maintain the false alarm probability constant over the operating ranges, the missed detection probability will be virtually zero at a high SNR. Even if it is possible to lower the false alarm probability to a number that is lower than the designed target, practically without sacrificing the missed detection probability at a high SNR, existing methods don't have ways to use different thresholds to change detection performance since existing methods use a fixed threshold regardless of the SNR.
Without an efficient detection mechanism, either more battery power is consumed, or a high miss rate is inevitable, thereby giving a poor communication performance. As such, there exists a need for improving existing methods for detecting paging indicators.